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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

i68

IRON

an agate mortar with 0-5 gram of ferro-chromiuin or ferro manganese, or 1-2
grams of the oxide with i gram of ferro-silicon, the mixture being introduced
quantitatively into the boat and the combustion carried out for i|--2 hours at
1050.

With readily fusible t'erro metallic alloys, sue.h as ferro-vanadium and ferro-
molybdenum, it is advisable to mix with a little refractory r.lay.

The above method of estimating the total carbon, which is coming more and
more into genera,! use, combines exactness with great rapidity (for ordinary pro-
ducts, 30 ,|o minutes sullice) and has the great advantage over the ('oriels method
that it. is applicable to any ferrous product.

(c) COITKU CULOKIDK MivinoD. This method consists in attacking
the. iron with a reagent, such us copper potassium chloride, which leaves
the carbon unchanged, and in determining the carbon separated by com-
bustion. It is less exact but simpler than the two preceding methods and
may always be. used with advantage tor products rich in carbon.

Sneh quantity of the finely powdered sample is taken as will liberate
about 0-015 0-02 gram of carbon : 3 grams of steel containing about 0-5%
of carbon, r gram of cast iron with not much more than ,!% of carbon, and
0-5 gram of products still richer in carbon.

An aqueous 30% solution of copper potassium chloride, is prepared as
free, as possible, from organic matter, 50 c,c. of this solution being used per
gram of metal to In1, attacked.

This volume, of the solution is placed in a ,130 c.e. conical 11 ask and
acidified with a little hydrochloric acid to prevent the dissolution of small
quantities of carbonaceous matter, the weighed sample being then added and
the, llask shaken. The. iron passes immediately into solution liberating
copper, which, however, dissolves completely in the excess of the reagent
on gentle heating and shaking, leaving a black residue containing the whole
of the, carbon. The action is usually complete in about half an hour.

Any basic iron salt fotmed is then dissolved by addition of a few drops
of hydrochloric acid and the liquid filtered through a ('touch crucible con-
taining ignited asbestos. If all the carbon is retained by the filter, dilution
of a few drops of the brown filtrate with water acidified with hydrochloric
acid yields a clear, greenish solution. The llask and residue are washed
first with dilute copper potassium chloride solution acidified with hydro-
chloric acid and then with distilled water until the wash wafer no longer
contains chloride, the crucible being then tided at a low temperature,

The asbestos with the carbon are. then burnt in a platinum boa! in a
combustion tube through which oxygen is. passed, the procedure being that
followed in ordinary elementary analysis of organic compounds. Between
the combustion tube, and the absorption bulbs for the carbon dioxide (Geisslur
bulbs), two U-tubes w inserted, one, with pumice soaked in sulphuric, acid
saturated with chromic acid to oxidise and retain any .sulphur dioxide
formed by oxidation of sulphur or sulphides, and the other copper sulphate
dehydrated at 200'"' to catch moisture and any traces of hydrochloric acid,
CO2 x 0-27273 -.-carbon.

For the combustion of the carbonaceous residue separated, the above; mulhod
may be replaced by treatment with chromic and .sulphuric. uuid.s in the Corleis
apparatus (see p. 164), Certain products, suuli as lurro Hthi'.on, fcrro chromium, 1-77                ---